1. Field of the Invention
The invention pertains to the field of blade tensioning. More particularly, the invention pertains to an improvement of the structure of a blade tensioner and a system that includes a blade tensioner that applies tension to the chain that drivingly connects the driven shaft within an engine to the driving shaft.
2. Description of Related Art
A blade tensioner has been used conventionally as the tensioner that applies tension to a chain. Generally, a blade tensioner consists principally of a resinous blade shoe having an arcuately curved chain sliding face, and metallic leaf spring-shaped blade springs that are disposed on the side opposite the chain sliding face of the blade shoe and that are used to exert a spring force on the blade shoe.
During chain operation, the chain travels while sliding along the chain sliding face of the blade shoe. At this time, the chain is subjected to compression loading as a result of the elastic resilience of the blade springs and the blade shoe, thereby tensioning the chain. When the chain slackens during operation, the blade springs, which deform elastically on the side where the radius of curvature increases, are subjected to return deformation on the side where the radius of curvature decreases, thereby causing the blade shoe to protrude into the chain side and take up the chain slack, so a constant, uniform tension is maintained in the chain.
There are numerous problems that arise involving how well the blade tensioner works. One such problem is damping efficiency. In an automobile engine, a blade tensioner as disclosed in prior art Japanese Patent Application Public Disclosure No. 2000-234656, and shown in FIG. 1, the blade tensioner (100) consists principally of the resinous blade shoe (101) having the arcuately curved chain sliding face (101a), the metallic leaf spring-shaped blade springs (102) that are disposed on the side opposite the chain sliding face (101a) of the blade shoe (101) and that are used to exert a spring force on the blade shoe (101), and the metallic support blade (103) that supports the blade shoe (101). Slots (110a) and (111a) are formed in the distal end portion (110) and the proximal end portion (111), respectively, of the blade shoe (101), and the ends of the blade springs (102) are inserted into and held within these slots. A pair of holes (103a)(103b), is formed in the support blade (103), and the support blade (103) is fastened within the engine by means of bolts inserted through these holes. The proximal end portion (111) of the blade shoe (101) is supported rotatably by the pin (104) fastened in the support plate (103). The lock washer (105) is installed on the pin (104). Support portion (130), which is equipped with the support face (130a) that slidably support the distal end portion (110) of the blade shoe (101), is provided at the end of the support plate (103).
As shown in prior art FIG. 2, the blade spring (102) has a radius of curvature ro smaller than the radius of curvature of the blade shoe (101). However, after the blade spring is mounted in the blade shoe (101), and the blade tensioner is installed in the engine, the radius of curvature of the blade spring (102) changes from ro to Ro ( greater than ro). That is, the blade spring (102) is elastically deformed, which applies compression loading to the chain as a result of the elastic resilience equivalent to the amount of its elastic deformation, thereby maintaining the tension of the chain.
After the chain elongates during operation, the blade springs (102), which deformed elastically on the side where the radius of curvature increases in order to apply compression loading to the chain, are subjected to return deformation on the side where the radius of curvature decreases, as the result of the restoring force. Consequently, the chain sliding face (101a) of the blade shoe (101) protrudes into the chain side, thereby taking up the chain slack.
Prior art FIG. 3 shows an example of the application of the aforementioned blade tensioner to a timing chain used to drive an engine""s overhead camshaft. In an engine""s timing chain, the chain span generally is long because the center-to-center distance between the crankshaft and camshaft is long. As a result, the overall length of the blade shoe (101) also is long. Plus, the proximal end portion (111) of the blade shoe (101) is provided so as to rotate freely around point O, the center of the support shaft (150) fastened to the engine side. The distal end portion (110) is provided so as to slide freely along the linear support face (160) disposed on the engine side. Before the timing chain elongates, the distal end portion (110) of the blade shoe (101) contacts point A on the support face (160). When the timing chain elongates, the restoring force of the blade springs causes the blade shoe (101) to deform so that it protrudes toward the chain span side. As a result, as shown by the dashed line in FIG. 2, the proximal end portion (111) of the blade shoe (101) rotates around point O, and the distal end portion (110) slides along the support face (160), so the contact point on the support face (160) moves to point B.
At points D and E on the support face (160), the compression forces exerted by the chain on the blade shoe (101) as reactions to the compression loads applied by the blade shoe (101) to the chain are, respectively, F and Fxe2x80x2. As for the, at point E the blade springs elastically deform as a result of the restoring force. This decreases the amount of elastic deformation, thereby also decreasing the compression load of the blade springs on the chain and results in the following inequality:
F greater than Fxe2x80x2xe2x80x83xe2x80x83(1) 
Furthermore, as shown in prior art FIG. 4, at point D, the compression force F of the chain produces the bending moment M (=Fxc3x97OA) that rotates the blade shoe around point O. Similarly, at point E, the compression force Fxe2x80x2 produces the bending moment Mxe2x80x2 (=Fxe2x80x2xc3x97OB) that rotates the blade shoe around point O.
At points D and E, the compression forces F, Fxe2x80x2 are decomposed into the direction parallel to the support face (160) and the direction orthogonal to the support face (160), and the angles formed by the directions in which the compression forces F, Fxe2x80x2 are exerted and the directions orthogonal to the support face are labeled xcex8 and xcex8xe2x80x2, respectively.
Of the compression force F at point D, F cos xcex8, the component orthogonal to the support face, is in equilibrium with the normal force N of the support face (160). Plus, the compression force F, F sin xcex8, the component parallel to the support face, is exerted in the direction that the blade shoe is slid along the support face (160). However, the force exerted against this F sin xcex8 is the frictional force xcexcN (i.e., xcexcFcos xcex8, where xcexc is the coefficient of friction).
Similarly, of the compression force Fxe2x80x2 at point E, Fxe2x80x2 cos xcex8xe2x80x2, the component orthogonal to the support face, is in equilibrium with the normal force Nxe2x80x2 of the support face (160). Also, of the compression force Fxe2x80x2, Fxe2x80x2 sin xcex8xe2x80x2, the component parallel to the support face, is exerted in the direction that the blade shoe is slid along the support face (160). The force exerted against this Fxe2x80x2 sin xcex8xe2x80x2 is the frictional force xcexcNxe2x80x2 (i.e., xcexcFxe2x80x2 cos xcex8xe2x80x2).
Here xcex8xe2x80x2 greater than xcex8, so
cos xcex8xe2x80x2 less than cos xcex8
Also, from (1),
Fxe2x80x2 less than F 
so
xcexcFxe2x80x2 cos xcex8xe2x80x2 less than xcexcF cos xcex8
Therefore,
xcexcNxe2x80x2 less than xcexcNxe2x80x83xe2x80x83(2) 
From (2), it is evident that the frictional force is less at point E than at point D.
However, when tension fluctuation and chain rattling during operation induce chord or harmonic vibration in the blade tensioner, each blade spring in the blade shoe is subjected to repeated elastic deformation and return deformation. At this time, a damping force is generated by the sliding together of each blade spring. Also, recent research has revealed that the sliding resistance between the blade shoe""s distal end portion and the support face also contributes to the blade tensioner""s ability to dampen (i.e., control) the chain""s chord or harmonic vibration.
Furthermore, when the chain is elongated in a conventional blade tensioner, the frictional force exerted between the support face and the distal end portion of the blade tensioner decreases considerably, which results in a problem; the damping efficiency of the blade tensioner drops.
Another problem associated with blade tensioners is the tilting of the blade tensioner in a sideways direction during operation. An example of the application of a blade tensioner as viewed from the chain sliding face side of the blade shoe to the timing chain that drives an engine""s overhead camshaft is shown in prior art FIG. 5. The blade shoe (50) and the chain (60) travels along the chain sliding face (50a) of the blade shoe (50), through-hole (51a), which is formed in the base (51) of the blade shoe (50), and the shoulder bolt (70) inserted into the through-hole 51a. The shoulder bolt (70) is screwed into the screw hole formed in the cylinder block (71) of the engine.
According to this configuration, the blade shoe (50) rotates freely around the shoulder bolt (70) in proportion to the elongation of the chain (60). The elastic resilience of the blade springs (not shown) varies, thereby changing the amount of displacement of the blade shoe (50) toward the chain (60), which applies the appropriate tension to the chain (60).
However, in order for the blade shoe (50) to rotate around the shoulder bolt (70), a constant clearance must be provided between the through-hole (51a) of the blade shoe (50) that supports the shoulder bolt (70) and the head exterior surface (70a) of the shoulder bolt (70).
Furthermore, the creation of such a clearance sometimes causes the blade shoe 50 to tilt sideways, as shown in prior art FIG. 6, because of the lateral, left and right in prior art FIG. 5, deflection of the chain during operation. In the case of a blade tensioner applied to a timing chain, the center-to-center distance between the driving shaft and the driven shaft generally is longer than in the case of a chain used to drive auxiliary equipment (e.g., an oil pump). So, the chain span is long, so the overall length of the blade shoe of the blade tensioner also becomes long. As a result, when the blade shoe tilts sideways, the deflection of the distal end of the blade shoe also increases, so the deflection r of the distal end reaches as much as approximately 3 mm.
Also, as shown in prior art FIG. 7, an enlargement of area IX in prior art FIG. 6, such tilting of the blade shoe causes edge (51b) to interfere with the head exterior surface (70a) of the shoulder bolt (70), sometimes causing the blade shoe (50) to lock with the shoulder bolt (70) in this state. The blade shoe (50) is then unable to rotate freely around the shoulder bolt (70). As a result, the blade shoe (50) is unable to displace toward the chain by exactly the appropriate amount in response to chain elongation, so it loses the ability to maintain the appropriate tension in the chain. The interference between the edge (51b) of the blade shoe (50) and the shoulder bolt (70) produces wear at edge (51b). This further enlarges the clearance between the shoulder bolt (70) and the through-hole (51a) of the blade shoe (50). As a result, the blade shoe (50) tilts farther sideways.
A third problem common to blade tensioners is regarding the rigidity of the blade shoe that can result from guide portions being associated with the chain. Chains used in applications with long center-to-center distances, such as the timing chain used to drive an engine""s overhead camshaft, the chain""s slack-side span lengthens, so the chain""s transverse deflection during operation increases. As a result, it sometimes is necessary to transversely guide the chain along the chain sliding surface.
In a hydraulic tensioner used in such applications, as shown in the cross-sectional view in prior art FIG. 8, guide portions (51)(52), that extend longitudinally along the shoe (i.e., in the direction perpendicular to the page on which the figure appears) are formed on the left and right sides of the chain sliding surface (50a) of the tensioner shoe (50). These guide portions (51)(52) control the transverse deflection of the chain (60), thereby guiding the travel of the chain 60. In the case of a blade tensioner the provision of guide portions (51)(52) increases the blade shoe""s flexural rigidity, thereby resulting in a defect: The blade shoe (50) becomes difficult to bend.
In order to apply the appropriate constant pressure to the chain associated with the blade tensioner, it generally is necessary for the blade shoe to bend readily so that the blade shoe""s radius of curvature can be varied according to the chain slackness. However, when such guide portions as guide portions (51)(52) are provided over the entire length of a blade shoe, it becomes difficult to bend the blade shoe, so the blade shoe""s radius of curvature cannot be varied as appropriate to the chain slackness. As a result, the appropriate constant tension cannot be applied to the chain.
The present invention improves the chain-damping efficiency in a blade tensioner applied to the chain within an engine, prevents the sideways tilt of the blade tensioner during operation, in a blade tensioner applied to the chain in an engine, and provides a blade tensioner with a functionality that allows it to transversely guide a chain along the chain sliding face in a blade shoe, while maintaining the flexural deformability (i.e., the flexibility) of the blade shoe. The blade tensioner of the present invention is part of a blade tensioner system for a chain that drivingly connects a driven shaft in an engine to a driving shaft of the engine with a blade shoe having a shoe proper that has an arcuately curved chain sliding face and left and right pair of guide portions on both sides of the chain sliding face that are used to guide the chain sliding along the chain sliding face in a transverse direction, where the guide portions extend continuously along the chain length of the sliding face. Plus, the guide portions have a height, a plate thickness, and a cross-sectional shape that inhibits an increase in flexural rigidity of the blade shoe. In addition, the blade shoe has a proximal end portion provided at the proximal side of the shoe proper so that the proximal end portion of the blade shoe can rotate freely around a support shaft inserted therethrough, and a distal end portion provided at the distal end of the shoe proper; so that the distal end portion of the blade shoe can rotate around the support shaft inserted therethrough, and is able to slide freely along the support face provided in the engine. Lastly, the blade shoe has leaf spring-shaped blade springs that are disposed on a side opposite the chain sliding face of the blade shoe that are used to exert a spring force on the blade shoe.